Optical instrument



J, a HENERSON OPTICAL INSTRUMENT Filed March 27, 19241 J 6 MA PatentedNov. 29, 1927.

PATENT OFFICE.

. JAMES BLACKLOCK HENDERSON, 0E BLACKHEATH, ENGLAND.

OPTICAL INSTRUMENT.

Application filed March 27, 1924, SeriaI No.

My invention relates to improvements in optical instruments such ascameras, te1e-' scopes or the like for use on aircraft or other movingbodies for observing or photographing terrestrial or elevated targets.It relates,

more particularly to the elimination of the apparent movement of theimage of the target in'the focal plane due to relative rectilinearmovement between the instrument and thetarget. The inventionis'applicable posure. These movements may be angular due to banking,pitching or yawing of the aeroplane, or may be rectilinear due to thesubstantially rectilinear movements of the aeroplane in its forwardflight or lateral drift down-wind.

Taking it as axiomatic that a clear photograph has hitherto depended onpreventing apparent movement of the imageon the plate during exposureexceeding, say, 2 minutes of an altitude of 5000 feet above the target,the kn rate of movement of the image will be 68 are measured from thelens, then if the-speed of the aeroplane be 100 feet per second atminutes of are per second of time, the maximum possible exposure beingtherefore l/34th of a second. Other factors, however, such as rotationof the image due to yawing of the aeroplane may produce much more rapiddisplacement of the image, imposing still greater limits to the possibleduration of the exposure. z

' Practical remedies for the efi'ects of these movements have in thepast been confined to a shortening of the exposure, an increase of thephotographic speed of the plates used, and an increase of the diameterof lenses.

None of these remedies are completely sue- 702,250, and in Great BritainApril 17, 1923.

make. with accuracy and are very expensive.

I -approach the problem from another direction and instead of decreasingthe exposure to suit the movements of the ima e, I eliminate theapparent movement of t e image for a period sufficient to permit of thelength of exposure which atmospheric and other conditions demand. Iproduce in the focal plane of the camera an image of the target and Istabilize bothv the image and the photographic plate in that plane longenough to secure a good photograph.

To produce this stabilized imagefit is necessary to eliminate orcompensate the effects of all relative movements between the camera andtarget, both angular and rectilinear. In my co-pending applicationSerial No. 674,871, filed November 15, 1923, I have describedv how Icompensate angular movements of the'aeroplane to which the camera isattached and the present invention relates to a method of compensatingfor rectilinear movements so that compensation will be complete. It alsoincludes the application of the measurement of the compensation todetermine:-

i (a) the groundspeed of the aeroplane at a known altitude, or

(-6) the altitude,- when the groundspeed is own. An embodiment of myinvention is shown in the attached drawings in which,

Fig. 1 isan elevation of a photographic camera and the mechanism used toproduce a stabilized image. a

Fig. 2. is a half plan of Fig. 1.-

Figs.'3, 4, and 5 show details not clearly shown in Fig. 1.

In Figs. 1 and 2 I haveincluded the mechanism' shown in connection withmy 00- ending application Serial No. 674,871, file November 15, 1923, asa comprehension of the present invention entails a description of theformer.

In Figs. 1 and 2, 1 is a gyroscope in its casing with an approximatelyvertical rotor axis, pivoted on trunnions 2 in a gimbal ring 4'wh1ch inturn is pivoted on trunnions 5 and 6 in two opposite sides of a. squareframe 7 the trunnions being hollow. .The 15, the arm 35 being equal andparallel to other two sides of the frame 7 are prolonged in arms 8 and 9which carry horizontal trunnions 10 supported in bearings in two pillars12 an a main frame 13. The frame 7. is supported at its other end by theframe 13 on anadjustable support 14 which will bedsscribed more fullylater.

In ball bearings in the hollow trunnion 5- is a spindle 15, (also seeFig. 3) which carries at one end inside the gimbal ring 4 a smallhorizontal fork 16 and at its other end outside the frame-7 a largerhorizontal fork 17 at the end of a. U-shaped neck 17 -shown more clearlyin Fig. 2. The fork 17 carries a rism 18 in its frame 19 on pivots 20which are collinear with the trunnion axis 1011. The prism is a rightangle prism with a roof rism on its hypotenuse, the two pentagonal acesbeing vertical and horizontal and the roof-edge uppermost and towardsthe gyroscope. In the outer end of the 5pmdle 15 is drilled an axialhole in which are housed a helical spring 21 and a pin 22 which is agoodsliding fit in thehole. Arms 23 and 24 attached to the trunnion 5 andspindle 15 respectively carry dprojections 25 and 26 which have machineclined to the vertical plane of t e trunnion axis 56. Between these'faces is a double roller 27 pivoted. on a vertical pillar 28 .mounted onthe outer end of the pin 22. The rollers 27 thus act as a key betweenthe trunnion. 5- andthe spindle 15, that is to say between the gimbalring 4 and the prism 18 as regards movement round the trunnion axis5-6.- In other words the prism 18 will be stabilized by the gyroscopeabout the axis 5--6. The two arms 23 and 24 are kept ressed against therollers 27 by a spring, w ich has been omitted for the sake ofclearness.

In the small fork 16 a bent arm 30 is pivoted on an axis pin 31, the armspanning the oscope in the vertical plane of the trunnion axis 5-6 andtermmating in adistant from the gyro trunnion axis 2 with the resultthat if the frame 7 tilts around the gyroscope about that axis,'the arm30 will move angularly about the pivot 31 rela-- tively to the framethrough half the angle of angular movement of the frame. The arm 30 iscontinued below the fork 16 in a short' arm 35 which is connected to apair of eccentric trunnions 36 on the prism frame 19 by a link and fork37 parallel to the spindle faces oppositely inthe distance of thetrunnion axis 36 from the prism axis 20. Angular movement of the arms 30and 35 round the pivot 31 will therefore be communicated in equal amountand direction to the prism 18. That is to say,

the prism 18 will be semi-stabilized about the axis 20. i

The camera 40 isrigidly attached to the plane of the camera a stabilizedimage of the. 1

ground vertically beneath the prism, irrespective of pitching androlling of the aeroplane, but rotates the image on the late through theangle of bank or yaw o the aeroplane. To counteract the lattermovementsI "pivot the back of the camera which carries the focal plane shutter 42and plate holder 42 on the camera body by a cylindrical cell 43 on theshutter fitting in a circular bearing in the back of the body 44, thepivot axis being the line of collimation of the lens. I control thepivoted back about this axis by a differential gear 45 which is actuatedb either of the repeater motors 46 and 47. T e motor 46 is connected bywiring (not shdwn) to a transmitter 48 on the spindle of a small D. C.follow-up motor 49, t e toothed pinion 50 of which gears with a toothedsector 51 pivoted on a boss on the frame 7 (see Fig. 4.) concentricallywith the trunnion6. The D. C; motor is actuated (through wiring notshown) by a roller contact 52 onthe gimbal ring and a 2-part commutator53 'on the sector 51, so that the motor will move the sector through theangle of roll of the aeroplane, a similar displacement beingsimultaneously. imparted tothe transmitter 48 and through it to therepeater motor 46, differential gear 45 and shutter 42. The incidentalgearing is selected to give to the shutter an angular displacement equaland opposite to the roll of the aeroplane. As the aeroplane rolls,therefore, moving the camera angularly in relation to the stabilizedimage, the action of the follow-up motor and repeater motor keeps theshutter and plate stationary so that there is no relative movementbetween'the plate and the image. Similarly in the case of the rotationof the image e plate produced by ya'wing, I compensate this'byactuatingthe other repeater motor 47 in an exactly similar way from a ro-compassor other azimuth indicator got shown) carried by the aeroplane.

By the above means the compensation or elimination of all angularmovements of the aeroplane is complete, and it only 'emai'ns speed.

to counteract the effects of the rectilinear movement of the aeroplanein flight.

Asthe time between exposure in a continuous survey is very short Iemploy a twolens camera, or a reflex camera as shown, the ground glassviewfinder-60 being situated in the roof of the camera and the imagerefiected onto it by a mirror 61 pivoted inside the camera body andcapable of being raised out of the way into the position shown whenmaking an exposure or dropped into aposition inclined at 45 to the lineof collimation when using the view-finder. I pivot the view-finder cell62 on a ring attached to the top of the camera and key it to therotating shutter by the bevel gears 63, 64, so that both move throughthe same angle.

I first of all eliminate the effect of lateral drift of the aeroplane bypivoting the whole apparatus so far described on a vertical pillar 65 ona bed-plate 66 rigidly attached to the aeroplane and move it round thatpivot until the image in the view-finder is seen to be moving verticallydown the view-finder, lines such as 67 being marked on the ground glassfor the purpose. The camera is then clamped by means of the j am-nut 68or some similar device. A pointer 69 on the camera or its frame and ascale of degrees 69" on the base plate, situated in any convenient placewill give the deviation of the course from the compass heading of theaeroplane. This reading gives, in conjunction with the compass reading,the direction of the ground As ex lained above the prism 18 iscontrolled a out its trunnion axis 20 by the gyroscope through. thelever 30, arm 35 and link 37 so as to be moved through half the angle ofmovement of the aeroplane or frame 7 round the gyro trunnion axis 2. Byintroducing a movement of the frame 7 relatively to the camera I cantherefore produce a movement of the prism about its axis 26 which willcause a movement of the image vertically on the plate; I thereforearrange for such a movement equal to the apparent movement of the image,and in the opposite direction, so that for a short time the Image willbe stationary, the exposure being made during one of such periods. Thismovement I introduce by a D. C. motor 70, running at constant speeddrivin a variable speed gear 71, the slider of whic has a compoundcontrol by two setting levers 7 2 and 73, one of which I set at thestart for altitude and the other I adjust for ground speed. The drivenshaft 74 of the variable speedgear has a square end on which is slidablymounted a sleeve 75, which at one end is a cylinder and the other end acam, the .two curves being blended into each other along the length ofthe sleeve 75. The sleeve can be'slid along the square end- 74 by aforked lever 76 piv oted on the main frame 13. .Two pillars 77 (see alsoFig. 5) on the frame 13 form guides for a slide 78 on which a lug 7 9 onthe outer frame 7 of the gyro is adjustably supported by the screw 14,the slide 78 being provided on its lower face with a roller 80 whichrests on one or the other'curve of the sleeve according to the positionof the lever 76. \V'hen the roller rests on the cylindrical end of thesleeve 75 there will be no movementof the frame 7 relatively to theaeroplane and the image will have its usual steady downimage will beretarded, annulled or reversed according as the reverse movement due tothe tilting of the prism is less than, equal to or greater than movementdue to ground speed. If the variable speed gear has the setting lever 72properly set to the altitude on commencing a flight and the camera correctly oriented for direction of ground speed as described above, thesetting of the lever 7 3 which is observed to produce periods ofimmobility of the image in the view finder will therefore indicate thevelocity of the ground speed. I arrange the cam on the sleeve 7 5 togive a rapid lift to the frame 7 and a comparatively slow regular fall,producing a quick downward jump of the image. on the view-finderfollowed by a longer period of rest, so as to give a maximum time forthe observer to select his target, check the various settings and makethe exposures. From time to time he will have to move the lever 76 tobring the cylindrical end of the sleeve 75 under the roller 80 in orderto check the verticality of the prism 18. This is effected by two smalltelescopes and 91 on thecover 92 of the instrument by which thehorizonin. two perpendicular directions can be viewed in the two prisms 93, 94carried by the lever 30. If the gyro strays fr om the vertical the imageseen in the view-finder 60 just the prism 18 about both its pivot axes.The adjustmentabout its trunnion axis 20 is eifected by the screwadjustment 14 by which the frame 7 rests on the slide 78 (Fig. 5) andabout the trunnion axis 5-6 the prlsm in its fork 17 is adjustable, asshown in Fig. 2, by a screw" 95 passing through the trunnion 10 of theframe 7 and bearing against the tail of the bell-crank 96 the head of.whic bears against the end of the pin 22, COI ItEtCLiBIDg maintained bythe spring 21 (Fig. 3). By turning the screw 95 the pm 22 can be-movedin or out of its housing,

- will be no longer that of the ground vertically beneath and tocompensate for this I adproducing movement of the rollers 27 in the Vmade by the faces 25 and 26, and s0 adjusting the prism 18' angularlyround the axis 56. If the gyro 1 and gimbal ring 3, stray from thehorizontal plane, these two adjustments enable the observer by viewingthe horizon in the telescopes 90 and' 91 to adjust the prism 18relatively to the gyro so as to obviate straying of the line of sightfrom the vertical. Butwhen making these ad'ustments the roller 80 mustrest on the cy 'ndrical end of the sleeve 75 so as to have no motion ofthe frame 7 in which the aeroplane and telescopes 90 and 91 donotpartici ate.

ese observations do not in any way in"- terfere with the work of takingphotographs, while the complete stabilization of the image on the plateenables exposures to be prolonged so that telephotographic or wideanglelensesmay be used, or exposure made in weather conditions in which;otherwise photographs could not be taken at all.

In Fig. 1, I show a D. C. motor 70, running at constant" eed, thevariation for ground speed being-introduced into the variable speed gearcompounded with the altitude. Alternatively I may use a variable s edmotor and have only one control of ti: variable speed gear. For instanceI may drive the motor proportionally to the altitude and set thereduction gear for round speed, or vice versa. In another orm I may evendrive the variable speed gear from the aeroplane engine or byclockworkor by an air-screw, but the last form would not be reliable as it wouldhave a velocity proportional to the airspeed, not the groundspeed. Inall forms 'the equation of the movement given to the prism is the same v5 v-{ in which a isthe movement given to the ima e on the plate by thetilt of the prism, I the groundspeed, the focal length-of a camera lensand h t e altitude,

so that the displacement of the image, v=f

in which fis a constant for a given lens. Where cameras with differentlenses have to be used for different purposes, I either providedifferent cams for the variable speed gear, or else introduce an 7factor into the control of the motor or variable speed gear.Interchangeable cams .would, however be the simpler method. A number ofdifferent cams could be arranged along the sleeve 75 if desired, any ofwhich could be brought into use by the lever 76.

I may release the camera shutter by a Bowden wire or trigger worked bythe downward travel of thejrame 7 so that the exposure could beaccurately timed by the mechanism itself and s?) avoid the jumpoccurring before the exposure was complete.

The trigger 'could be made so as to be generally out of action and thenbrought mto play whenvan exposure is required. I do not illustrate thisfeature as it can be done in so many obvious ways.

One of the main drawbacks of aerial photography in the past for surveypurposes has been the impossibility of plotting contours. With theapparatus described above however all photographs will be truly verticalas regards the central 'point and two 'consecutive photographs takenwith an overlap willhave equally oblique views of the overlappingportion. If therefore in surveying a given strip'of country consecutivephotographs are made to have half overlaps and the overlaps of each pairof photographs are then viewed stereoscopically, it would be possible toplot in contours with sufficient accuracy.

It will of course be understood that the scope of my invention is notlimited to aircraft'cameras, but includes any optical instrument fromwhich it is desirable to eliminate the effects of relative movementbetween the instrument and the object in view. Also although I describethe case where the instrument is in action over a relatively stationaryterrestrial object, the conditions might be reversed without impairingthe utility of the instrument. In some cases both the instrument andobject might be in motion or one might be moving angularly while theother moves in the straight line. For example a camera as described,mounted on a ship rolling at anchor could, by a simple inversion of theprism 18, be used to photogra h an aeroplane flying overhead,eliminatlng the efiects of the ships rollin and of the aeroplan'esmovement through the air.

Having now ascertained and particularly described my said invention, andin what manner the same is to be performed I claim p 1. In an optical aparatus mounted on a rectilinearly moving body, the combination of anoptical part associated therewith, and

variable speed mechanism for moving said part in the plane of androportional to said rectilinear movement, w ereby the field of view inthe focal plane of said apparatus is immobilized.

2. The combination of an optical instrument for use on. a rectilinearlyand angularly moving body, gyroscopic means connected to an optical partof said instruments to nullify the angular movement of the image in thefocal plane, and means connected to said optical part to nullify therectilinear movement of the image in the focal plane of the instrument.7

3. An optical apparatus for use onv a variably moving body havingrelatively movable optical parts, a gyroscope for stabilizing said partsagainst angular movement, and

variable speed mechanism for moving said parts to immobilize the fieldof view against rectilinear movement.

4. The combination of an optical instrument for use on a rectilinearlyand angularly moving body, means to annul the effeet on the image ofsuch movement, said means comprising an optical part for saidinstrument, a gyroscope for stabilizing said part against angularmovement, and mechanism for moving said part in the plane of saidrectilinear movement to render the image stationary against rectilinearmovement.

5. The combination with an optical apparatus foruse on a moving body, anoptical member associated with said ap aratus, a gyroscope forstabilizing sai member against angular movement relative to the field ofview, means controlled by said gyroscope to annul rotary movement in thefocal plane'of the apparatus, and variable speed means connected to saidmember to eliminate rectilinear movement in the field of view of theapparatus.

6. An optical apparatus provided with external means to eliminaterelative movement between the apparatus and the field of view, saidmeans comprising a gyroscope, an optical member stabilized by thegyroscope, variable speed mechanism for actuating said member and saidgyroscope to annul rectilinear movement in the field of view, and meansoperated by said gyroscope for eliminating relative rotary movement inthe focal plane of the apparatus.

7. An optical apparatus for use on a rectilinearly moving body, variablespeed means for moving an optical member substantially in the plane ofthe rectilinear movement to render the field of view stationary,gyroscopic means for stabilizing the field of view, and means foradjusting the position of said apparatus to be substantially parallel tothe lane of the rectilinear movement of the 0d 8. An optical apparatusfor use on a rectilinearly moving body, an external optical partassociated with said apparatus, a gyroscope for stabilizing said partand mounted therewith, and variable speed means for moving saidreflector and said gyroscope substantially in the plane of saidrectilinear motion at a rate varying according-to a function of themovement of the body.

9. In an optical instrument foruse on a variably moving body, agyroscope for stabilizing the image against angular movement, a variablespeed mechanism for immobilizing the image against rectilinear movement,and means for compensating for the drift of the body.

10. An optical apparatus for use on a rectilinearly moving body, areflector associated with said apparatus, variable speed mechacalrelation therewith, a

nism 'for moving said reflector in the plane of said rectilinearmovement so as to immobilize the image in the focal plane of saidapparatus, and means associated with said mechanism for measuring thespeed of said rectilinear movement.

11. In combination with an optical apparatus for use on a substantiallyrectilinearly moving body having the line of collimation in the plane ofthe rectilinear movement, a gyroscope for stabilizing the field of viewof said apparatus, means for compensating for the'straying of saidgyroscope, mechanism for nullifying the efiect of the rectilinearmovement on the field of view of said apparatus, means for compensatingfor the drift of said body, and means for measuring the relative speedof said body.

12. An optical apparatus for use on a recti linearly moving b0comprising an optical instrument, an external optical part inoptiroscope, said part being associated with sai gyroscope whereby it-isstabilized, variable'speed mechanism for moving said yroscope and saidpart at a speedproportional to the speed of the body so as to'immobilize the field of view, means associated with said mechanism forindicating the speed of said body, and means for orienting thecollimation line of said apparatus parallel to the rectilinear movementof the body.

13. In an optical apparatus mounted on a relatively angularly andrectilinearly moving body, the combination of a gyroscope forstabilizing the field of view of sald apparatus against angularmovement, variable speed mechanism for immobilizin the field of view ofsaid apparatus against rectilinear movement, and indicating meansassociated with said mechanism for designating the speed of saidrectilinear movement.

14. In an optical apparatus mounted on a relatively angularly andrectilinearly movmg'body, the combination of a gyroscope for stabilizingthe field of view in the focal plane of t e apparatus against angularmovement, cam-actuated means for immobilizing the field of view in thefocal plane of the apparatus against rectilinear -movement, mechanismfor orienting said apparatus parallel to the rectilinear movement, andmeans associated with said mechanism for indicating the direction of therectilinear movement.

15. In an optical a paratus mounted on a rectilinearly moving ody, anexternal optical part in optical relation with said apparatus, mechanismfor moving said part in the plane of and proportional to the rate of therectilinear movement whereby the object in the field of view of saidapparatus is stabilized, and indicating means associated with saidmechanism for indicating the distance between the body and the objectaccording to view of the a paratus, said means comprising a function ofthe movement of said optical ratus, gyroscopic means for stabilizingsaid part. external reflector and means controlled by 16., In an opticalapparatus, a combination the yroscope for adjusting a member in the 10of a movable external reflector for the appafocal plane of the apparatusin accordance 5 ratus, means for immobilizing the field of with alateral movement of the'apparatus.

mechanism or bodily orienting the appa- JAMES BLACKLOCK HENDERSON.

